Bulkhead fittings are used as part of a system when it is necessary to pass a conduit, tube, or other similar apparatus through a fluid impermeable barrier or bulkhead. These bulkheads can be arranged to form fuel tanks, climate-controlled spaces, air containment units, which are intended to segregate either a liquid or a gas from a surrounding environment. These bulkhead fittings are furnished with redundant seals to prevent external fluid transfer or leakage through the bulkhead around the tube by means of o-rings, fay and fillet seals.
A bulkhead fitting traditionally functions by providing a robust and reliable connection to structure allowing fluid to be transmitted across the interface through a transport element tube. In hydraulic systems, the hydraulic fluid (and therefore hydraulic transfer element tube) may become heated to high temperatures. This high temperature may damage structure if there is a direct connection between the transfer element tube and the heat-sensitive structure. Heat may also deform or modify the interface between the bulkhead and conduit and compromise the sealing features of the fitting. Therefore, there have been developed means of thermally insulating the bulkhead fitting and conduit from the bulkhead, therefore preventing damage to the bulkhead.
One example of such thermal insulation is the use of a plastic insulator between the fitting and bulkhead. This barrier may be up to an inch thick on either side of the fitting, but provides sufficient insulation to prevent damage to the bulkhead. Another example is the use of a wide thermally conductive surface to dissipate the heat without creating a localized area of high temperature.
With the use of composite materials for aircraft, it may be necessary to utilize the hydraulic conduits as a means for transferring electrical energy due to lightning strikes or precipitation static. Because thermal insulating materials tend to also insulate against electricity, this method tends to not allow for a combined solution of thermal non-conductivity (to resist the flow of heat) with electrical conductivity (to pass the flow of electrical current from fitting to bulkhead) in the properties of the insulating materials in a hydraulic bulkhead fitting. To provide for electrical conductivity while providing thermal insulation, current may be diverted away from the hydraulic line.
Further, Federal Aviation Regulation (FAR) 25.981 requires a redundant system so that any single failure combined with a latent failure cannot result in an ignition source within the fuel tank of an aircraft. There is therefore recognized a need in the art for an improved bulkhead fitting assembly that satisfies FAR 25.981.
One method of overcoming this restriction has been the use of additional components included with a bulkhead fitting installation. Installing these additional parts can add time and weight to a bulkhead fitting installation but provide for protection against spark propagation. There is therefore proposed a novel bulkhead fitting assembly to overcome these problems and others in the prior art. The proposed assembly provides a combined solution in the insulation of materials using titanium metal (or equivalent) to provide a more efficient solution than the existing methods offering savings in weight and expense to a manufacturer.